Principle of the main condensation evaporator

Condensation and evaporation – I’ve never seen what’s inside actually

The main condensation evaporator is the only component responsible for heat exchange between the upper and lower columns; it serves as the core of the air separation unit. The working principle involves temperature difference transfer. Typically, the liquid oxygen in the main cooler is at around -177 degrees Celsius, while the temperature in the upper part of the lower column is around -174 degrees Celsius; thus, the temperature difference in the main cooler is 3 degrees

There are many types of configurations for primary cooling systems: tubular types, including long tubes and short tubes; membrane types; and plate-fin types. Nowadays, plate-fin types are the most commonly used. The principle behind them is simple – nitrogen from the lower tower exchanges heat with liquid oxygen from the upper tower, thereby providing reflux liquid for the lower tower and rising gas for the upper tower. The temperature difference is between 2 and 3 degrees

Taking advantage of the different boiling points of oxygen and nitrogen at various pressures, the nitrogen in the lower column is condensed to provide reflux liquid for both columns, while the liquid oxygen in the upper column evaporates to supply rising steam to the upper column.

1) The main condenser serves as a link between the upper column and the lower column; it is used for heat exchange between the liquid oxygen at the bottom of the upper column and the gaseous nitrogen rising from the top of the lower column. 2) Liquid oxygen absorbs heat in the main condenser and evaporates into gaseous oxygen ； Gaseous nitrogen releases heat in the main condenser and is condensed into liquid nitrogen; part of it is taken as a product, part is used as reflux liquid for the lower column, and another part is sent to the upper column as reflux liquid after being throttled. 3) Since the pressure in the lower column is higher than that in the upper column, the saturation temperature of gaseous nitrogen in the lower column is higher than that of liquid oxygen in the upper column. Liquid oxygen absorbs the latent heat of condensation released by gaseous nitrogen and evaporates; hence it is called a \"condensation evaporator\".

The main condenser is a type of shell-and-tube heat exchanger, used for heat exchange between the liquid oxygen at the bottom of the upper column and the gaseous nitrogen rising from the top of the lower column. In the main condenser, the temperature of the gaseous nitrogen in the lower column is higher than that of the liquid oxygen in the upper column; therefore, the gaseous nitrogen at the top of the lower column enters the main condenser where it is condensed into liquid nitrogen (some of which is taken as a product, some serves as reflux liquid for the lower column, and another portion is sent back to the upper column as reflux liquid after being throttled). The liquid oxygen at the bottom of the upper column enters the main condenser where it is evaporated into gaseous oxygen (some of which is used as an oxygen product, while the rest is used as the vapor for distillation in the upper column). Additionally, at standard atmospheric pressure, the boiling point of liquid nitrogen is -195.8°C, the boiling point of liquid oxygen is -183°C, and the boiling point of nitrogen is lower than that of oxygen. In the main condenser, however, the boiling point of nitrogen is higher than that of oxygen, as the pressure in the lower column is higher than that in the upper column; consequently, the saturated temperature of gaseous nitrogen in the lower column is higher than the saturated temperature of liquid oxygen in the upper column (the saturated temperature of a gas is proportional to its pressure)

Who has a 3D diagram of the main cooler? It would be more intuitive!

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The classics upstairs – all are classics! Everything has been said very well! Primary cooling is the evaporation of oxygen and the condensation of nitrogen!